To be clear, I am not advocating simply having a group. Your organization should also have a company page within LinkedIn but these two pages serve different purposes. Your LinkedIn company page is generally a place where interested users can keep up with your company updates or find out general information about your organization. Your LinkedIn group should be a place for a real community where users can interact not only with you, but also with one another. Furthermore, your LinkedIn group can be a place that might gather far more attention than your company page and thereby help you increase your organization's exposure.
In conclusion, if your professional based organization doesn't already have a LinkedIn company page and group, then you should start both of them today.
Does your group have a LinkedIn page? How is it used?